Sylvia Allegreto of the University of California at Berkeley found last year that the six children of Walmart founders Sam and James “Bud” Walton had the same net worth in 2007 as the bottom 30 percent of American households. But between 2007 and 2010, that net worth rose, while the incomes of most Americans declined, explaining the three-year shift, Bivens notes.

While Walmart heirs are some of the wealthiest people in the world — two of them are among the top five world’s richest women, according to Wealth X — many of the employees that work with the company likely fall among that bottom 40 percent of American earners. The company has driven down American wages by outsourcing much of its distribution work to warehouses across the country, according to a recent report from the National Employment Law Project.

In addition, bringing a new Walmart to town may cost a community big time in lost wages. A planned Seattle-area Walmart could cost the area $14.5 million in lost wages over the next 20 years, a local advocacy group found in April.

The discrepancy between the Waltons’ wealth and that of the rest of the country may be huge, but it’s just one example of the prevalence of income inequality in America. The top one percent of American earners saw their incomes spike 275 percentbetween 1979 and 2007, while the bottom one-fifth of Americans saw their wealth grow by only 20 percent during the same period, according to the Congressional Budget Office. In addition, the top 10 percent of U.S. earners control two-thirds of the country’s wealth.